Method of making rotary threaded fasteners



Dm .319 E. J. SKIERSKI 3,550,255 Y v METHOD-0F MAKING ROTAR? THREADEDFASTENERS Filed July 5, 1968 i 2 Sheets-Sheet 1 Int/en for fdwinJfikiers/ci By his Allorney E. J. SKIERSKI METHOD OF MAKING ROTARYTHREADED FASTENERS Filed July 5. 1968 2 Sheets-Sheet 2 US. Cl. 29-557 2Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing a selfdrilling and thread forming screw comprising annealing a screw blank,punching a pilot end on the leading end of said screw blank by means ofdies which form flutes in said leading end, and simultaneously formingthreads on the screw blank and removing excess material resulting fromthe punching step from the pilot end by means of finishing dies.

Complementary finishing dies for use in the method of this'inventioncomprising a first die having a thread forming member and a deburringmember and cam member for removing excess material. A second die havinga thread forming member and a deburring member.

The present application is a continuation-in-part of United Statesapplication for Letters Patent Serial No. 579,036, filed Sept. 13, 1966,now Patent No, 3,395,603.

This invention relates to a method and dies for manufacturing a rotarythreaded fastener or screw having novel features which permit the screwto cut a pilot hole and swage threads therein without the need for anypredrilling or the like.

Normal practice in forming cutting edges on the pilot end or enteringportion of a screw is to machine grooves or slots, of a shape dictatedby the particular design, in a screw blank without altering the shape ofthe resultant land portions intermediate the grooves. That is, theconventional circular cross-section screw blank generally has twocutting edges milled therein but the remaining portion of thecircumference of the blank at the pilot end is left in an arcuate formcorresponding in curvature and diameter to the main shank body. As aresult, these lands or arcuate portions engage the member into which thescrew is inserted during the cutting operation. This engagementincreases the torque required to perform the cutting operation due tothe frictional drag forces resulting from such engagement. The methodand apparatus of the present invention provide means for manufacturingan improved screw having a pilot end of essentially ellipticaltransverse configuration therein the cutting edges define the major axisof the elipse and the intermediate lands define the minor axis. Withthis improved construction, the lands do not engage a member in which apilot hole is cut, thus minimizing the torque required for insertion.

As noted above, normal practice has been to machine the cutting edges inthe pilot end of the screw blank. This is a relatively costly operation.Dies are employed to pinch or punch the cutting edges in screwsmanufactored in accordance with the present invention. The novel methodwhich permits this practice and the unique dies and thread forming meansused in the method provide a relatively inexpensive means ofmanufacturing screws of this type at a production rate heretoforeimpossible.

Accordingly, it is an object of this invention to provide a relativelylow cost method of manufacturing a United States Patent iasltener havingan entering portion for cutting a pilot It is a further object of thisinvention to provide unique dies for threading a screw and removingexcess material from the pilot end thereof.

To this end and in accordance with a feature of this invention there isprovided a method of manufacturing a drilling and thread forming screwcomprising annealing a screw blank, punching a pilot end on the leadingend of said screw blank by means of dies which form flutes in saidleading end, and forming threads on said screw blank.

In accordance with a further feature of this invention, novelcomplementary dies are provided for threading the shank of a screw andremoving excess material from the pilot end thereof.

The above and other features of the invention, together with variousnovel details of construction, will now be more particularly describedwith reference to the accompanying drawings and pointed out in theclaims. It is to be understood that the particular embodiment of theinvention shown in the drawings is for illustration purposes only and isnot to be construed as a limitation of the invention.

In the drawings:

FIG. 1 is a side elevation of a metal screw blank prior to punching andthreading;

FIG. 2 is a side elevation of the screw blank following the pointing orpunching operation and prior to the threading operation;

FIG. 3 is a side elevation of a completed metal screw which is formed bythreading the screw blank shown in FIG. 2;

FIG. 4 is a perspective view of a pair of dies particularly constructedto perform the punching operation the results of which are shown in FIG.2;

FIG. 5 is an enlarged view of the screw illustrated in FIG. 3 as viewedfrom a angle;

FIG. 6 is an end view of the entering portion or pilot end illustratedin FIGS. 3 and 5;

FIG. 7 is a perspective view of the pilot end of the screw shown inFIGS. 3, 5 and 6;

FIG. 8 is a perspective view of the complementary finishing diesemployed in the method of this invention, a screw being shown inposition prior to the thread rolling operation and the dies spaced apartto facilitate illustration thereof;

FIG. 9 is a perspective view similar to FIG. 8 with the screw inengagement with one of the said dies; and

FIG. 10 is a perspective view similar to FIG. 9 with the screw at anadvanced location relative to said dies.

In order fully to appreciate the advantages of the subject invention, anunderstanding of the fastener produced thereby is necessary.Accordingly, the specification will initially describe the preferredembodiment of a screw disclosed in the aforementioned application as anexample of products which may be manufactured by the present invention.

A preferred embodiment of the screw 10 is illustrated in FIGS. 3, 5, 6and 7. As shown in FIG. 3 the screw 10 comprises an elongated shank 12having a head section 14 integral with a trailing end thereof. The headsection may be provided with any convenient, conventional meanscooperative with a tool for turning the screw to effect insertion orwithdrawal.

The screw 10 has a pilot end 20 of substantially elliptical transverseconfiguration as viewed in FIG. 6. The term elliptical is here used forpurposes of description or visualization only and it is not intended ina strict mathematical sense. Longitudinally extending flutes or slots22, 24 of similar construction are formed in opposite quadrants of thepilot end. The flute 22 is defined by a cutting surface 26 havingcutting edges 28, 30 and by a drag surface 32. The flute 24 is definedby a cutting surface 34 having cutting edges 36, 38 and by a dragsurface 40. The cutting surfaces 26 and 34 are, preferably, slightlyarcuate and lie generally in a plane which has a small amount ofangularity with respect to the longitudinal axis of the screw whereby tofacilitate removal of material from the cutting edges during the cuttingoperation. The contours of the surfaces 26 and 34, as best seen in FIGS.and 6, provide the proper cutting angle and rake at the cutting edges 28and 36. The drag surfaces 32 and 40 are also angularly disposed withrespect to the longitudinal axis of the screw to facilitate discharge ofmaterial removed in the cutting operation.

As most clearly indicated in FIG. 6, the maximum width of the cuttingsurfaces 26 and 34 is greater than the maximum width of the dragsurfaces 32 and 40. That is, the cutting surfaces 26, 34 lie generallyoffset from and parallel to the transverse major axis a of theelliptical pilot end whereby essentially to define the major axis. Thedrag surfaces lie in a similar relation to the transverse axis 12.Accordingly, a pilot hole cut *by the cooperative action of the cuttingedges 28, 30 and 36, 38 of the cutting surfaces 26 and 34, respectivelywill be of greater diameter than the minor axis 12 of the pilot end.Thus, the drag surfaces 32 and 40 which may be considered to define theminor axis b will not engage the sidewalls of a pilot hole cut by thecutting edges. Similarly, the arcuate portions of the pilot endintermediate the cutting and drag surfaces, hereinafter referred to aslands 46 and 48, will also not engage the sidewalls of a pilot hole.That is, the lands 46, 48 progress transversely in generally arcuatecontour from a minimum radius at the drag surfaces to a maximum radiusat the cutting surface. A difference of approximately in the length ofthe major and minor axis has been found adequate to ensure clearance bythe lands 46 and 48, and, accordingly, is preferred.

The construction just discussed thus provides a self cutting screw whichmay be used to cut a pilot hole by the application of substantially lessdriving torque than required to insert screws disclosed by the priorart. Frictional drag has been reduced to a minimum. The only frictionalforces are those necessary to accomplish the cutting operation.

The lands 46 and 48, see particularly FIG. 7, are generally bulbous inlongitudinal contour. This construction allows maximum reinforcement forthe cutting surfaces 26 and 34 which essentially constitute a leadingend of the lands. That is, the bulbous or convex contour of the landspermit the provision of a maximum amount of material to absorb theforces generated by the cutting operation and the maintenance of theelliptical configuration discussed above.

As best illustrated in FIG. 3, in the preferred embodiment the cuttingedges 30 and 38 are tapered toward the trailing end of the screw. Thatis, the transverse major axis of the generally elliptical pilot enddecreases in length in the direction of the trailing end. This alsofacilitates the escape of material removed during the cutting operationand decreases the effective cutting contact area whereby to minimizefrictional drag.

Helical thread convolutions 50 are formed on the trailing portion of theshank. In the preferred embodiment, the major axis a of the generallyelliptical pilot end is of greater length than the root diameter of thethreads on the shank 12, see particularly FIG. 3. Thus, the pilot endwill cut a pilot hole of greater diameter than the root diameter of theshank 12. In the preferred embodiment, the transverse major axis of thepilot end has a maximum length at its widest point equal toapproximately the root diameter plus one-half of the difference betweenthe crest and root diameters. Thus,

the pilot end cuts a pilot hole larger than is actually necessary.However, this size pilot hole permits the threads 50 to swage thematerial engaged by the crest portions of the threads into the voidsproximate to the root diameter of the shank whereby to achieve completecontact of the threads 50 with the member in which the screw isinserted. This construction reduces the cutting or swaging which must becompleted by the threads 50 and thereby reduces the required drivingtorque.

The elliptical configuration discussed in relation to the pilot end 20extends to and includes that portion of the threaded shank whichcomprises the first two threads adjacent the pilot end, i.e. in thepreferred embodiment. Thus, the initial threading or tapping of thepilot hole is accomplished by what may be defined as lobes 54 spaced 180apart on each of the first two threads. The lobes 54 are located at themajor axis of the elliptical cross-section. That is, the portions of thefirst two threads at the minor axis have a larger land width andtherefore a lower crest height than at the major axis. Compare FIGS. 3and 5 in this regard. This construction substantially reduces thedriving torque required for insertion and improves the strippingqualities. The lobes 54 effect progressive internal threading of thepilot hole with a minimum frictional contact during the initial phase ofthread forming.

The pilot end 20 is provided with a pointed tip 60 which aids in initialpositioning and cutting. The tip 60 extends slightly in advance of thecutting edges 28, 36.

The novel screw structure described above readily could be produced byemploying standard machining practices to mill the flutes 22 and 24,etc. However, as in other applications where such standard practices areused, the cost would be high. Applicant has developed a unique method ofmanufacturing his fastener by the utilization of punching dies 71, 72shown in FIG. 4 and finishing dies 90, 92 illustrated in FIGS. 8, to 10.A primary obstacle to the use of the dies 71, 72, however, is that ifthe dies are employed on a screw blank without preparatory treatment,the blank will be hardened and crack under the pressures generated inthe use of the dies. That is, if a standard screw blank is exposed tothe pinching or punching pressures exerted by the dies 71, 72, the blankwill crack in the vicinity of the flutes 22, 24 and will be of otherwisepoor quality.

Applicant has found that if he anneals a screw blank, such as indicatedby 74 of FIG. 1, he is able successfully to form a screw of excellentquality. The result of the use of the dies 71, 72 on the blank 74 isshown in FIG. 2. The annealing operation lends sufficient ductility topermit the metal to flow whereby to form ears 76, 78 and a head on theblank 74. The ductility of the blank 74 enables it to withstand thepressures of forming without cracking at the points of maximum stress.The ears 76, 78 and the head 80 remain integral with the blank 74 afterthe die-punching operation and prevent abrasion of the cutting edgesprior to the threading or finishing step.

The dies 71 and 72 are preferably used with the apparatus described inmy copending application for Letters Patent of the United States No.675,999, filed Sept. 20, 1967, now Patent No. 3,398,413.

After the blank 74 is punched, the shank portion is threaded, the ears76, 78 removed and the head 80 removed by use of the complementaryfinishing dies 90, 92 as hereafter discussed. The die comprises a threadforming member 94, a deburring member 98 and a cam member 100. The die92 comprises a thread forming member .102 and deburring member 104respectively complementary to the members 94 and 98 of the die and ofsimilar construction. Accordingly, the discussion to follow will bedirected to the die 90 for simplicity, it being understood that thecomplementary members of the die 92 are of similar construction. Thedies are shown in spaced relation in FIGS. 8 to 10 to permitillustration of their operation. In actual use, the dies would bemounted in standard die holding apparatus and have a standard spacingand stroke.

The thread forming member 94 has a plurality of conventional threadforming grooves 106 formed on a surface thereof. The height a of thethread-forming member may be varied to accommodate screws of differentlength. That is, the height a of the thread-forming member is determinedby the length of screw shank to be threaded. As shown pictorially inFIGS. 8 to 10, the die 92 is movable relative to the die 90 toaccomplish threading of the shank of a screw blank. As stated aboverelative to the preferred embodiment of a screw manufactured pursuant tothis invention, a portion of the shank next adjacent the pilot end isdeformed into elliptical configuration in the punching operationdiscussed above. Exposure of this elliptical portion of the shank to thethread-forming action of the complementary dies produces lobes 54 inaccordance with the above described construction.

The deburring member 98 of the die 90 dimensionally corresponds to thethread-forming member 94 except for the height b thereof. The deburringmember functions to remove the ears 76, 78 from a screw during thethreading operation and, therefore, the height [2 is determined by theheight of the ears 76, 78 formed on a particular screw blank size. Thework engaging surface 110 of the deburring member comprises an elongatedflat surface. In use, the dies 90 and 92 are positioned in standard dieholding apparatus such that the members 98 and 104 will be in verticalalinement with the ears 76, 78 of a screw to be threaded. Conventionalspacing means may be used in this regard and to compensate for themember 100 associated with the die 90 whereby vertically to aline thecomplementary die members. The ears 76 and 78 are broken away from thescrew blank during the thread-forming stroke of the die 92 by engagementwith the members 98 and 104 as illustrated in FIG. 9. Sharp cuttingedges are provided as a result of this operation.

The cam member 100 removes the head 80 of a screw during the stroke ofthe die 92. The cam member corresponds dimensionally to the member 94except for a cam portion 106 projecting therefrom in position to engagethe head 80 of a screw located in threading relation between the dies90, 92. As illustrated in FIG. 10, engage- 6 ment of the head with thecam portion 106 causes the head 80 to be broken off during the stroke ofthe die 92.

Applicants above described novel method of pinching or punching thepilot end of a fastener and the removal of excess material therefrompermits the impartation of a variety of configurations thereto. Themethod may be used to produce self-cutting screws at a production rateheretofore impossible and at a lower unit cost.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent of the United States is:

1. A method of manufacturing a drilling and thread forming screwcomprising annealing a screw blank, punching a pilot end on the leadingend of said screw blank by means of dies which form flutes in saidleading end, said annealing step providing suflicient ductility topermit the flow of metal to form longitudinal ears on the side of thescrew blank and a head on the leading end in the punching step wherebyto avoid excessive stress at the points of maximum stress concentrationduring the punching operation, forming threads on said screw blank andremoving said ears and head to provide sharp cutting edges.

2. A method of manufacturing a drilling and thread forming screwaccording to claim 1 wherein said ears and head are removed by meansengageable therewith during exposure of the screw blank to threadforming means.

References Cited UNITED STATES PATENTS 3,318,182 5/1967 Carlson 1()103,218,656 11/1965 Reiland 10-1O 3,241,426 3/1966 Gutshall 47 3,395,6038/1968 Skierski 1O10X 3,463,045 8/1969 Prescott 10-10X JOHN F. CAMPBELL,Primary Examiner R. I. CRAIG, Assistant Examiner US. Cl. X.R.

